1. Field of the Invention
This invention relates to organopolysiloxane compositions and more particularly, to room temperature vulcanizable organopolysiloxane compositions which are capable of yielding cured products having a good resistance to oil and are particularly useful as a sealing material for foamed in place gasket (FIPG) systems of automobiles.
2. Description of the Prior Art
Sealing in and around engines of automobiles has been heretofore made using oil-resistant gaskets and/or packings made of cork, organic rubbers, asbestos and the like. However, disadvantages are involved in that these materials are rather expensive, and stock and process controls of these gaskets and packings are complicated, coupled with another disadvantage that the sealing properties are not necessarily satisfactory.
To avoid the above disadvantage, the FIPG system using room temperature vulcanizable silicone rubbers has been now adopted, and good results are obtained with respect to workability, sealability and heat resistance. Because of the recent trend toward a low fuel cost, gear oils used in transmissions of automobiles are being replaced by oils of the low viscosity multi-grade type containing large amounts of extreme pressure additives. This causes the problem that the molding made of the organopolysiloxane rubber deteriorates when used over a long term at high temperatures, thus causing oil leakage.
In order to solve the above problem involved in the room temperature vulcanizable silicone rubbers, Japanese Laid-open patent application No. 57-76055 proposes the use of reinforcing silica and magnesium oxide having a specific surface area of not less than 50 m.sup.2 /g in combination with the silicone rubbers. Moreover, Japanese Laid-open patent application No. 59-80463 describes the addition of zinc carbonate or zinc oxide to the rubbers. In the recent automobile industry, high performance engine oils or gear oils which contain large amounts of extreme pressure additives are employed. In addition, it is required that the FIPG sealing material have good durability and adhesiveness at high temperatures. In this regard, the known silicone rubber compositions are not satisfactory.